Primer 1 · Objects, functions and vectors

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Three ideas carry the whole of Day 1: R stores things in objects, you do things with functions, and the commonest object is a vector. Run the cells, change the numbers, break them on purpose. For the full explanation of any of this, see the R primer.

Objects

<- is the assignment arrow. It puts the thing on its right into the name on its left.

Change 240 to your own department’s intake and run it again.

Functions

A function is a verb. It takes arguments in brackets, separated by commas.

Named arguments like digits = 2 are clearer than positional ones. Prefer them.

Vectors

c() combines values into a vector: a column of values, all of the same type. It is the most-used function in R.

A comparison returns a logical vector, one TRUE or FALSE per element:

A vector holds one type. Mix them and everything is silently converted to the most permissive type, a classic source of confusion:

Those quotation marks mean all three are now text. You cannot take the mean of that.

NoteExercise 1: your first vector

Time: 5 minutes

Five students sat an OSCE station and scored 78, 70, 91, 55 and 83. Put those marks into a vector called osce.

osce <- c(78, 70, 91, 55, 83) 
osce <- c(78, 70, 91, 55, 83)

c() combines values. The marks go inside the brackets, separated by commas.

NoteExercise 2: summarise the marks

Time: 5 minutes

How many of those five marks are 70 or above? A comparison gives you TRUE and FALSE, and sum() counts TRUE as 1.

osce <- c(78, 70, 91, 55, 83) sum(osce >= 70) 
osce <- c(78, 70, 91, 55, 83)

sum(osce >= 70)

You do not need a loop. osce >= 70 compares every element at once.

Check yourself

NoteFour questions on the Moodle course

Take Check yourself · Primer 1 on the Moodle course. Four questions, unlimited attempts, no marks. Every answer comes back with an explanation, so a wrong one costs you nothing and teaches you something.

Next

→ Primer 2 · Tibbles: put those vectors side by side into the rectangle you will actually analyse.

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